Cerebral cavernous malformations (CCM), characterized by dilated sinusoidal vascular spaces lined by a single layer of endothelium, affect the central nervous system and may lead to neurological problems including bleeding and seizures. Mutations in the three genes, CCM1 (KRIT1, Krev1/Rap1a Interaction Trapped 1), CCM2 (OSM, malcavernin) and CCM3 (PDCD10, Programmed Cell Death Protein 10) have been shown to cause CCM. While recent in vitro studies have begun to illuminate the nature of CCM signaling, an in vivo, mechanistic understanding of CCM pathophysiology is lacking. Based on our recent data from in vitro cell culture studies, in vivo data from our mouse conditional knock-out of Ccm3 in neural cells, and intriguing observations in animal models from various groups, we hypothesize that CCM3 is a negative modulator of Akt signaling via interactions with PP2A, and CCM lesions are the consequence of altered expression of Akt and its downstream effectors. We further hypothesize that CCM3 signaling mediates an interaction between neural and endothelial cells and alteration of this interaction caused by neural CCM3 loss, results in a vascular phenotype. We propose to test these hypotheses using in vitro and in vivo approaches aimed at elaborating this novel Ccm3 signaling pathway and to investigate its potential influence on the interactions among various cell types within the neurovascular unit in CCM lesion development. We will perform studies aimed at clarifying the nature of Ccm3 interactions with the Akt signaling pathway. We will comprehensively study the mx1-Cre;Ccm3lox/lox mouse model that we have recently generated. Unlike other conditional Ccm3 knockouts, these mice survive long term and develop vascular pathology. The vascular pathology is characterized by dilated vessels throughout the brain and isolated lesions that are reminiscent of human CCM disease. We will take advantage of our findings to gain insight into CCM3 function and signaling. In addition, we propose to cross inducible VE-cadherin-CreER and GFAP-CreER to Ccm3lox/lox mice to study cell autonomous effects of CCM3 in endothelial cells and postnatal astrocytes. The proposed experiments are focused on identifying the molecular pathways relevant to CCM disease and on studying these pathways in vivo with a long-term goal of defining new and more effective therapies.